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| author | Thomas Munro <tmunro@postgresql.org> | 2020-10-12 20:41:16 +1300 |
|---|---|---|
| committer | Thomas Munro <tmunro@postgresql.org> | 2020-10-13 00:26:49 +1300 |
| commit | f0f13a3a08b2757997410f3a1c38bdc22973c525 (patch) | |
| tree | 47a4364849b5bdafb0e0e7ba6f33fe471feda985 /src/backend/optimizer/util/pathnode.c | |
| parent | 3fb676504da9c019540c7384423c7e3d7d394110 (diff) | |
| download | postgresql-f0f13a3a08b2757997410f3a1c38bdc22973c525.tar.gz postgresql-f0f13a3a08b2757997410f3a1c38bdc22973c525.zip | |
Fix estimates for ModifyTable paths without RETURNING.
In the past, we always estimated that a ModifyTable node would emit the
same number of rows as its subpaths. Without a RETURNING clause, the
correct estimate is zero. Fix, in preparation for a proposed parallel
write patch that is sensitive to that number.
A remaining problem is that for RETURNING queries, the estimated width
is based on subpath output rather than the RETURNING tlist.
Reviewed-by: Greg Nancarrow <gregn4422@gmail.com>
Discussion: https://postgr.es/m/CAJcOf-cXnB5cnMKqWEp2E2z7Mvcd04iLVmV%3DqpFJrR3AcrTS3g%40mail.gmail.com
Diffstat (limited to 'src/backend/optimizer/util/pathnode.c')
| -rw-r--r-- | src/backend/optimizer/util/pathnode.c | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c index c1fc866cbf9..5281a2f9983 100644 --- a/src/backend/optimizer/util/pathnode.c +++ b/src/backend/optimizer/util/pathnode.c @@ -3583,15 +3583,18 @@ create_modifytable_path(PlannerInfo *root, RelOptInfo *rel, if (lc == list_head(subpaths)) /* first node? */ pathnode->path.startup_cost = subpath->startup_cost; pathnode->path.total_cost += subpath->total_cost; - pathnode->path.rows += subpath->rows; - total_size += subpath->pathtarget->width * subpath->rows; + if (returningLists != NIL) + { + pathnode->path.rows += subpath->rows; + total_size += subpath->pathtarget->width * subpath->rows; + } } /* * Set width to the average width of the subpath outputs. XXX this is - * totally wrong: we should report zero if no RETURNING, else an average - * of the RETURNING tlist widths. But it's what happened historically, - * and improving it is a task for another day. + * totally wrong: we should return an average of the RETURNING tlist + * widths. But it's what happened historically, and improving it is a task + * for another day. */ if (pathnode->path.rows > 0) total_size /= pathnode->path.rows; |